1. Field of the Invention
The invention in general relates to the demodulation of digital amplitude-modulated carrier signals, notably to such signals which are received with great differences in field strength.
2. Discussion of the Related Art
The demodulation of amplitude-modulated carrier signals of highly variable field strength takes place, for example in broadcast receivers. Therein, the signals are amplified by a variable-gain amplifier in such a manner that they exhibit approximately the same level for different incoming field strengths at the demodulator. This principle of variable or controlled amplification, however, cannot be used in some other cases.
An example in this respect is a data carrier which can be read and written in a contactless manner and which cooperates with a fixed base station which transmits a carrier signal whereby not only data for controlling notably the data carrier, but also the energy for operating the circuits provided in the data carrier are transferred. Therefore, as the received energy increases, for example due to a decreasing distance between the data carrier and the base station, the voltage output by the aerial must be limited to a maximum value. However, it is difficult to derive the information contained in the amplitude modulation from the limited aerial signal by demodulation in such a case. Moreover, amplitude-modulated carrier signals are very susceptible to interference.